Since multiple migrations are a Bad Thing for the poor question-asker (and apparently may violate some key concepts of quantum mechanics and cause Al Gore to become angry), and seeing as how we now have a cool rejected migration system that tracks and handles these things, the ability to double-migrate questions should really be disabled by technical means rather than just an administrative prohibition.

This could be accomplished in several ways - the most logical seems to be having the "Off-Topic" close reason for questions that were migrated default to plain-vanilla-off-topic and not bother showing the migration list.

It already does this for regular users. It's moderators that are the problem here.
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ChrisFOct 16 '12 at 20:20

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@ChrisF We should never be trusted with special powers
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voretaq7Oct 16 '12 at 20:21

Sorry, what do you mean by multiple migrations? Just migrating a question from site A to site B, which migrates it to site C?
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NullUserException อ_อOct 16 '12 at 20:22

@NullUserExceptionอ_อ yeah - basically if SO migrates something to SF and SF's mods then kick it to SU the world ends...
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voretaq7Oct 16 '12 at 20:23

I reckon that a question that's been bounced around this much probably won't be a good question, but what if there are legitimate reasons to do so? Say something gets migrated to SO from SU, but after further review and comments, it really belongs on SF. Do you just want to block the possibility of migrating it again?
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NullUserException อ_อOct 16 '12 at 20:26

@NullUserExceptionอ_อ the preferred path is for the intermediate site to reject the migration, and the original site to send it to its proper end destination. (In practice these ARE usually crap questions and SHOULD have been killed at their origin site, but occasionally a bad user migration escapes before mods can step in and send it to a good home...)
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voretaq7Oct 16 '12 at 21:04

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please pay heed to @ChrisF -- this is only possible if the moderator is the one making the mistake.
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Jeff Atwood♦Oct 17 '12 at 9:47

That could work too - maybe somehow tack a comment on the originating site's question telling them why the migration was rejected (and what site the receiving site thought should get it). Not sure how much extra complexity that adds for implementation though...
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voretaq7Oct 16 '12 at 20:21